An electrical or power substation can involve electricity transmission and distribution systems where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between a generating plant and a consumer or load, and the voltage may be transformed in several steps.
Industrial setups can involve intense energy consumption and include one or multiple dedicated substations including both an upstream substation connecting to the main source of power (either the grid or the in-house generator) and downstream substations for distribution of power to different load centers distributed over various parts of industries. In addition, the industry may have its own generation system to meet its energy demand and also have power management system for effectively handling power for its purpose.
Power management functionality includes load shedding, power and voltage control, power restoration, power source synchronization, etc. that depend on measurements like voltage, current, power and other power-quality parameters for effective handling of power demands for various equipment and processes, power fluctuations, equipment constraints, etc. It is known to find these kinds of power management functions within industrial setups like process industries such as refineries and power utilities. However, such a setup is also applicable to other process industries such as cement, pulp and paper, petrochemical plants, fertilizers, steel, mining and metals, water and waste water treatment plants, etc.
The substations (both upstream and downstream) can include several power and distribution transformers, cabling, switching, reactive power and grounding equipment. This equipment should be protected against power system anomalies like power surges, power system faults, etc. Such protection can be accomplished by Intelligent Electronic Devices (IEDs) that provide different comprehensive protection and monitoring functions. Besides protection and monitoring functions, IEDs can also offer metering and control functions. The IEDs are microprocessor-based devices that are associated with power system equipment, such as circuit breakers, generators, transformers, power lines, power cables, reactors, motors, capacitor banks, etc. IEDs can receive primary power system information like voltage and current from sensors to perform various protection and monitoring functions. Known types of IEDs include protective relaying devices, load tap changer controllers, circuit breaker controllers, recloser controllers, voltage regulators, secondary functions like load shedding, etc. where the load shedding functionality is implemented in an IED and process data exchange for such a functionality is done by the primary IEDs that directly interface with the power system equipment, controllers, etc. Thus, an IED can perform several power system functions depending on its purpose.
Substation automation can be an important and complex aspect to solve power system function tasks, using state of the art technologies. By doing so,
Substation automation can provide value added features to perform automatic control based on power system conditions/events, equipment maintenance, communication of substation information to higher level control systems like Grid Control Centers, etc. Through the Substation automation, manual and automatic control command functions are provided such as closing and opening of switching equipment (circuit breakers and disconnectors), or raising/lowering voltage levels in order to maintain desired voltage levels. Multiple communication protocols exist for substation automation, which include many proprietary protocols with custom communication links. However, interoperation of devices from different vendors is highly desired for simplicity in implementation and use of substation automation devices.
The IEC61850 standard from the International Electrotechnical Commission (IEC) advocates interoperability amongst Intelligent Electronic Devices (IEDs) from various manufacturers using known engineering models (for example, IEC61850 Common Engineering Model using Logical Nodes), data formats and communication protocols. Recent IEDs are therefore designed to support the IEC61850 standard for substation automation, which provides interoperability and advanced communications capabilities like GOOSE (Generic Object Oriented Substation Event) and MMS (Manufacturing Message System) communication profiles.
The power management functionality like load shedding is currently implemented as a centralized function in the substation automation systems for process industries like refineries, petrochemical plants, steel plants, cement, pulp and papers, etc. The load shedding or shedding of load referred herein generally implies cutting off the power on certain lines/loads, when the power demand becomes greater than the power supply. This can happen on the occurrence of a power system fault or an event that would affect the power available to feed the processes in an electrical network.
Centralized implementation of the above function, such as when implemented in a single process controller IED and deployed at the upstream substation, can have several short comings. For example, centralized function implementation can cause high loading due to centralization of all functions for the complete power system network, where load shedding is to be deployed. It also can result in high and sustained levels of communication loads in the process controller IED, as it would collect desired data from downstream IEDs for execution of the centralized function. This can lead to lower availability of the process controller IED for other activities. Since the downstream IEDs are directly connected to the central process controller, it is directly exposed to the complexity of the substation configurations and connectivity.
Further, overload situations in power equipment, such as a downstream transformer, cannot be easily detected in the centralized implementation and hence there may be no facility for downstream substation slow load shedding to lessen overloading on the power equipment. Slow Load Shedding may be based on overload of grid (public grid) transformer(s) or interconnecting transformer(s) to a substation. Contemporary power management solutions encompass a grid transformer overload load shedding functionality and there is no overload handling for interconnecting transformers between upstream and downstream substations. In an event of the grid transformer being overloaded, the central process controller sheds loads to correct the overload condition and in the event of interconnecting transformers being overloaded, the overload protection may get activated and isolate the transformer resulting in lower availability of the interconnecting transformer.
Exemplary embodiments disclosed herein are directed to developing a power management system and technique that can allow for improved power management by managing overloading of power equipment such as, interconnecting transformer(s), and effective slow load shedding in the system to provide higher system availability.